Method for removal of poisonous gases

ABSTRACT

Hydrides of As, B, P, Sb or Se in a gas can easily be removed from the gas by contacting the gas with an adsorbent consisting of activated carbon containing: 
     (1) copper oxide and 
     (2) at least one of (a), (b) and (c) selected from the group consisting of 
     (a) at least one alkali metal compound, and 
     (b) at least one alkaline earth metal compound and 
     (c) at least one compound of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Cd and Pb.

The present invention relates to a method of treating poisonous gases containing hydrides of As, B, P, Sb or Se.

Although hydrides such as AsH₃, B₂ H₆, PH₃, SbH₃ and H₂ Se have been used in large quantities as raw material gas for the production of semiconductors, fumigation gas, etc., such hydrides, even in trace amounts, are extremely noxious to the human body, and efficient removal of these hydrides from gases is strongly demanded.

As the method of removing hydrides of As, B, P, Sb and Se in gases, there have been proposed processes of washing with chemical solutions such as oxidizing solutions or methods of adsorption by use of activated carbon, etc. and the like. Nevertheless, such processes and methods exhibit poor removal effect, and efficient adsorbents have long been wanted.

The present inventors, in view of such circumstances, conducted intensive investigation, and as a result, found that arsines in fluids can be removed very efficiently by using an activated carbon containing copper oxides and alkali metal compounds, alkaline earth metal compounds or metal compounds of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Cd nd Pb, which has culminated in the present invention.

Thus, the present invention relates to a method for the removal of at least one hydride of As, B, P, Sb and Se from a gas containing the same, which comprises contacting the gas with an activated carbon containing:

(1) copper oxide (hereinafter referred to in some instances as "First Component") and

(2) at least one of (a), (b) and (c) (hereinafter referred to in some instances as "Second Component") selected from the group consisting of

(a) at least one alkali metal compound,

(b) at least one alkaline earth metal compound and

(c) at least one compound of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Cd and Pb.

In the present method, an activated carbon containing First and Second Components is used as adsorbent. The adsorbent can be prepared by allowing activated carbon to contain First and Second Components.

The activated carbon may be any type of activated carbon, if it is produced by the known processes with coal, coke, charcoal, coconut shells, resins, etc. employed as raw material and shows a specific surface area of 200 to 2000 m² /g; with reference to its shape or form, use is made of proper-shaped activated carbon, such as spherical- or cylindrical-shaped, crushed, powdered and fiber-like, depending upon the treatment method of gases.

The copper oxide which is employable as the First Component in the present invention may be either cuprous or cupric oxide.

Examples of the alkali metal compound, which is one of the Second Components, include inorganic acid salts or inorganic compounds of Li, Na, K, Rb and Cs, such as hydrogencarbonates, carbonates, nitrates, borates, silicates, sulfates, halides and hydroxides, and organic acid salts thereof, such as formates, acetates, oxalates, benzoates, salts of phenols and salts of sulfonic acids.

Examples of the alkaline earth metal compound, which is another Second Component, include inorganic acid salts or inorganic compounds of Be, Mg, Ca, Sr and Ba, such as carbonates, nitrates, sulfates, phosphates, halides, oxides and hydroxides, and organic acid salts thereof, such as formates, acetates and oxalates.

Examples of the compounds of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Cd and Pb, which are still other Second Components, include inorganic acid salts or inorganic compounds of these metals, such as carbonates, hydrogencarbonates, nitrates, borates, silicates, sulfates, phosphates, halides, hydroxides, ammonium salts and oxides, and organic acid salts, such as formates, acetates, oxalates, benzoates, salts of phenols and salts of sulfonic acids.

Though the adsorbents used in the present invention consist of an activated carbon containing the First and Second Components, the Second Component may be composed of an alkali metal compound [hereinafter referred to in some instances as "Component (a)"] solely, an alkaline earth metal compound [hereinafter referred to in some instances as "Component (b)"] alone or compounds of Al, Cr, Ti, V, Mn, Fe, Co, Ni, Zn, Cd and Pb [hereinafter referred to in some instances as "Component (c)"] solely, or also may comprise two kinds of these components, such as the Components (a) and (b), Components (b) and (c) and Components (c) and (a), or may consist of three kinds of the components, the Components (a), (b) and (c). In addition, the adsorbents may contain at least two compounds as the First Component, and may contain two or more components within the same Component group as the Second Components, for example two different components within the group of the Component (a).

The content of the First Component in the activated carbon containing metal compounds is 0.1 mg-atom to 3.0 mg-atom as metal per g of activated carbon, preferably 0.2 mg-atom to 2.0 mg-atom, while the content of the Second Component is 0.1 mg-atom to 5.0 mg-atom as metal per g of activated carbon, preferably 0.2 mg-atom to 4.0 mg-atom.

Each of the components contained in the activated carbon may be either supported or deposited on activated carbon, and the adsorbent may be made by adding each of the components to a raw material for activated carbon and activating the mixture. Furthermore, the adsorbents may be produced by adding part of the First and Second Components to a raw material for activated carbon and activating the mixture, followed by depositing the remainder of the Components on the resulting activated product. In cases in which the Components (b) and (c) to be deposited as the Second Component on activated carbon are other than oxides and the Component (a) is other than hydroxides, carbonates and hydrogencarbonates, it is desirable to conduct drying or calcining after the deposition.

With reference to the method of depositing each of the components on activated carbon, a procedure of impregnating or spraying activated carbon with a solution or suspension of each of the components in water (inclusive of aqueous acid or alkali solutions) or a variety of solvents may be used. In the above preparation process, meanwhile, the term "drying" denotes a step of evaporating the water or solvent in activated carbon deposited with the metal compounds at a temperature of not more than about 130° C., while the expression "calcining" means a step of heating the dried activated carbon deposited with the metal compounds in an atmosphere of inert gas, carbon dioxide gas, steam, combustion waste gas, etc. at a temperature of not less than 130° C. to thermally decompose the metal compounds partially or wholly.

Also, the activated carbon supported with copper oxide can be obtained by depositing on activated carbon inorganic acid salts or inorganic compounds of copper such as carbonates, basic carbonates, nitrates, sulphates, phosphates, halides, and hydroxides and organic acid salt thereof such as formates, acetates and oxalates in place of the First Component, and then calcining the mixture at a temperature of not less than 130° C. to convert only part of or all of these salts into copper oxide. The adsorbents of the present invention containing the First and Second Components can be produced by performing the deposition of the Second Components, before, after or simultaneously with, the calcining.

The method of the present invention is conducted by contacting a gas containing hydrides of As, B, P, Sb and Se with the activated carbon containing the metal compounds as obtained by the above procedure. The objective substances, which are to be removed by the present method, are hydrides of As, B, P, Sb and Se, such as AsH₃, B₂ H₆, PH₃, SbH₃ and H₂ Se.

As the procedure of contacting, use is made of the known means, such as the fixed bed, moving bed and fluidized bed. In such cases, the contacting temperature is not more than 200° C., preferably 0° to 150° C., while the pressure is not more than 50 kg/cm², preferably 0.1 to 40 kg/cm². The contacting time is 1/10 to 100 seconds as converted at 25° C. and 1 kg/cm², preferably 1/5 to 80 seconds.

The contact of the poisonous gas with the activated carbon in the present method can be conducted in the absence or presence of oxygen. Thus the method of the present invention can be applied to the treatment of not only a poisonous gas containing oxygen but also a posisonous gas not containing oxygen. Though hydrides of As, B, P, Sb or Se can be removed to a certain extent from a poisonous gas containing oxygen by a known method in which activated carbon not containing any metal compound is used, the hydrides are hardly removable from a poisonous gas not containing oxygen by the known method. Therefore, the method of the present invention is advantageously applied to the treatment of a poisonous gas not containing oxygen.

The examples described below illustrate the present invention more specifically.

EXAMPLE 1

Activated carbon A₀ of 16 to 24 mesh having the BET specific surface area of 1,150 m² /g was sprayed uniformly with aqueous solutions containing a given amount each of the First Component (copper nitrate) and the Second Component (nitrate of an alkali metal, nitrate of an alkaline earth metal and nitrate of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Cd or Pb (or sulphate for V alone).

50 ml of the resultant activated carbon deposited with the metal compounds was packed into a 4 cmφ column made of quartz glass, which was then heated at a heating rate of 5° C./min while passing nitrogen gas at a linear flow rate of 10 cm/sec, followed by calcining at 300° C. for 30 minutes.

The content of each of the metal compounds in the resultant adsorbent was 0.2 to 2.0 mg-atom as respective metals per g of activated carbon, as shown in Table 1.

By following the same procedure as described above, as control reference, activated carbon A₀ was deposited with nitrate of each metal alone, and calcined in a nitrogen gas at 300° C. for 30 minutes to prepare adsorbents.

15 ml each of the adsorbents as obtained in this manner was packed into a 6 cmφ column made of glass, respectively, and a gas(N₂ -97.5 vol. % and H₂ O-2.5 vol.%) of 30° C. containing 12 ppm of PH₃ was passed through the columns at a linear flow rate of 40 cm/sec to conduct the breakthrough adsorption tests for PH₃. The removal percentages for PH₃ at different times were measured, and the results are shown in Table 1.

EXAMPLE 2

Packed into a 1.6 cmφ column made of glass was 20 ml each of the adsorbents of Example 1, A₀ A₁, A₃, A₉, B₂, B₃, C₄, C₆, C₉, D₂, D₃, D₈, D₁₀, D₁₂, D₁₃, D₁₄ and D₁₅, and a gas (N₂ -97.5 vol. % and H₂ O-2.5 vol.%) of 30° C. containing 10 ppm of B₂ H₆, 10 ppm of H₂ Se or 10 ppm of SbH₃ was passed through the columns at a linear flow rate of 30 cm/sec to conduct the breakthrough adsorption test for B₂ H₆ and H₂ Se or SbH₃ with each of the adsorbents alone. The length of time required until B₂ H₆ and H₂ Se or SbH₃ leaked out of the column (the length of time for which breakthrough ratio of respective hydride compounds reached 5%) was measured, and the results are shown in Table 2.

EXAMPLE 3

Activated carbon A of 16 to 24 mesh having the BET specific surface area of 1040 m² /g was sprayed uniformly with aqueous solutions containing a given amount each of the First Component (copper nitrate) and the Second Component (nitrate of an alkali metal, nitrate of an alkaline earth metal and nitrate of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Cd or Pb (or sulphate for V alone).

50 ml of the resultant activated carbon deposited with the metal compounds was packed into a 4 cmφ column made of quartz glass, which was heated at a heating rate of 5° C./min while passing a nitrogen gas at a linear flow rate of 10 cm/sec, followed by calcining at 300° C. for 30 minutes.

The content of each of the metal compounds in the resultant adsorbents was 0.2 to 2.0 mg-atom as respective metals per g of activated carbon, as shown in Table 3.

By following the same procedure as described above, as control reference, activated carbon A was deposited with nitrate of each metal alone, and calcined in a nitrogen gas at 300° C. for 30 minutes to prepare adsorbents.

20 ml each of the adsorbents as obtained in this manner, A through L and ○1 through ○40 , were packed into a 1.6 cmφ column made of glass, and a gas (N₂ -97.5 vol.% and H₂ O-2.5 vol.%) of 30° C. containing 30 ppm of AsH₃ was passed through the columns at a linear flow rate of 20 cm/sec to conduct the breakthrough adsorption tests for AsH₃. The length of time required until AsH₃ leaked out of the column (the length of time for which the breakthrough ratio reached 5%) was measured, and the results are shown in Table 3.

                  TABLE 1                                                          ______________________________________                                                  Amount               Percent removal                                           of       The second  of pH.sub.3 at the                                        Copper   component; and                                                                             elapsed time                                     Adsorbent                                                                               (mg-     its amount  shown below (%)                                  No.      atom/g)  (mg-atom/g) 5 hrs                                                                               10 hrs                                                                               30 hrs                                ______________________________________                                         A.sub.0 (Control)                                                                       0        0            2    0     0                                    A.sub.1 (Control)                                                                       2.0      0            95   50   15                                    A.sub.2 (Control)                                                                       0        Na-2.0       58   31   23                                    A.sub.3 (Control)                                                                       0        K-2.0        59   35   20                                    A.sub.4 (Control)                                                                       0        Mg-2.0       48   20   15                                    A.sub.5 (Control)                                                                       0        Ca-2.0       45   34   15                                    A.sub.6 (Control)                                                                       0        Sr-2.0       40   23   10                                    A.sub.7 (Control)                                                                       0        Al-2.0       39   33   11                                    A.sub.8 (Control)                                                                       0        Cr-2.0       50   39   25                                    A.sub.9 (Control)                                                                       0        Fe-2.0       45   30   18                                    A.sub.10 (Control)                                                                      0        Ni-2.0       48   19   11                                    A.sub.11 (Control)                                                                      0        Pb-2.0       40   21   12                                    B.sub.1 (The                                                                            1.0      Na-1.0      100   98   50                                    present                                                                        invention                                                                      B.sub.2 (The                                                                            1.0      K-1.0       100  100   68                                    present                                                                        invention)                                                                     B.sub.3 (The                                                                            1.0      Mg-1.0      100  100   75                                    present                                                                        invention)                                                                     B.sub.4 (The                                                                            1.0      Ca-1.0      100  100   63                                    present                                                                        invention)                                                                     B.sub.5 (The                                                                            1.0      Sr-1.0      100  100   54                                    present                                                                        invention)                                                                     C.sub.1 (The                                                                            1.0      Al-1.0      100  100   63                                    present                                                                        invention)                                                                     C.sub.2 (The                                                                            1.0      Ti-1.0      100  100   54                                    present                                                                        invention)                                                                     C.sub.3 (The                                                                            1.0      V-1.0       100  100   50                                    present                                                                        invention)                                                                     C.sub.4 (The                                                                            1.0      Cr-1.0      100  100   73                                    present                                                                        invention)                                                                     C.sub.5 (The                                                                            1.0      Mn-1.0      100  100   41                                    present                                                                        invention)                                                                     C.sub.6 (The                                                                            1.0      Fe-1.0      100  100   29                                    present                                                                        invention)                                                                     C.sub.7 (The                                                                            1.0      Co-1.0      100  100   45                                    present                                                                        invention)                                                                     C.sub.8 (The                                                                            1.0      Ni-1.0      100  100   59                                    present                                                                        invention)                                                                     C.sub.9 (The                                                                            1.0      Zn-1.0      100  100   61                                    present                                                                        invention)                                                                     C.sub.10 (The                                                                           1.0      Cd-1.0      100   95   39                                    present                                                                        invention)                                                                     C.sub.11 (The                                                                           1.0      Pb-1.0      100   73   54                                    present                                                                        invention)                                                                     C.sub.12 (The                                                                           0.2      Cr-1.0      100   72   50                                    present                                                                        invention)                                                                     C.sub.13 (The                                                                           0.5      Cr-1.0      100   95   62                                    present                                                                        invention)                                                                     C.sub.14 (The                                                                           2.0      Cr-1.0      100  100   80                                    present                                                                        invention)                                                                     D.sub.1 (The                                                                            1.0      Na-0.3, Al-0.5                                                                             100  100   95                                    present                                                                        invention)                                                                     D.sub.2 (The                                                                            1.0      K-0.3, V-0.5                                                                               100  100   100                                   present                                                                        invention)                                                                     D.sub.3 (The                                                                            1.0      K-0.3, Cr-0.5                                                                              100  100   100                                   present                                                                        invention)                                                                     D.sub.4 (The                                                                            1.0      K-0.3, Mn-0.5                                                                              100  100   100                                   present                                                                        invention)                                                                     D.sub.5 (The                                                                            1.0      K-0.3, Fe-0.5                                                                              100  100   100                                   present                                                                        invention)                                                                     D.sub.6 (The                                                                            1.0      Mg-0.3, Co-0.5                                                                             100  100   100                                   present                                                                        invention)                                                                     D.sub.7 (The                                                                            1.0      Ca-0.3, Ni-0.5                                                                             100  100   100                                   present                                                                        invention)                                                                     D.sub.8 The                                                                             1.0      K-0.3, Zn-0.5                                                                              100  100   100                                   present                                                                        invention)                                                                     D.sub.9 (The                                                                            1.0      Na-0.3, Cd-0.5                                                                             100  100   95                                    present                                                                        invention)                                                                     D.sub.10 (The                                                                           1.0      K-0.3, Pb-0.5                                                                              100  100   88                                    present                                                                        invention)                                                                     D.sub.11 (The                                                                           0.2      K-0.3, Cr-0.5                                                                              100   81   67                                    present                                                                        invention)                                                                     D.sub.12 (The                                                                           0.5      K-0.3, Mn-0.5                                                                              100   99   83                                    present                                                                        invention)                                                                     D.sub. 13 (The                                                                          0.2      Mg-0.5, Cr-0.5                                                                             100   95   75                                    present                                                                        invention)                                                                     D.sub.14 (The                                                                           0.5      Mg-0.5, Cr-0.5                                                                             100   98   80                                    present                                                                        invention)                                                                     D.sub.15 (The                                                                           1.0      K-0.3, Mg-0.3                                                                              100  100   100                                   present           Cr-0.5, Fe-0.25                                              invention)                                                                     ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                                  The length of                                                                              The length of                                                                              The length of                                          time for    time for    time for                                               which the re-                                                                              which the re-                                                                              which the                                              moval percen-                                                                              moval percen-                                                                              breakthrough                                           tages for   tages for   ratio of SbH.sub.3                            Adsorbent                                                                               B.sub.2 H.sub.6 reached                                                                    H.sub.2 Se reached                                                                         reached 5%                                    No.      95% (hrs)   95% (hrs)   (hrs)                                         ______________________________________                                         A.sub.0 (Control)                                                                       1/6         1/4         1/3                                           A.sub.1 (Control)                                                                       11          15          15                                            A.sub.3 (Control)                                                                        6           7           9                                            A.sub.9 (Control)                                                                       15          11          11                                            B.sub.2 (The                                                                            38          35          30                                            present                                                                        invention)                                                                     B.sub.3 (The                                                                            45          40          41                                            present                                                                        invention)                                                                     C.sub.4 (The                                                                            40          40          39                                            present                                                                        invention)                                                                     C.sub.6 (The                                                                            52          45          41                                            present                                                                        invention)                                                                     C.sub.9 (The                                                                            48          43          47                                            present                                                                        invention)                                                                     D.sub.2 (The                                                                            67          59          63                                            present                                                                        invention)                                                                     D.sub.3 (The                                                                            85          71          90                                            present                                                                        invention)                                                                     D.sub.8 (The                                                                            71          75          62                                            present                                                                        invention)                                                                     D.sub.10 (The                                                                           60          73          58                                            present                                                                        invention)                                                                     D.sub.12 (The                                                                           83          79          65                                            present                                                                        invention)                                                                     D.sub.13 (The                                                                           68          68          60                                            present                                                                        invention)                                                                     D.sub.14 (The                                                                           80          78          79                                            present                                                                        invention)                                                                     D.sub.15 (The                                                                           103         105         110                                           present                                                                        invention)                                                                

                  TABLE 3                                                          ______________________________________                                                                           The length                                                                     of time for                                                                    which the                                                                      breakthrough                                             Amount of The second  ratio of                                                 Copper    component; and                                                                             AsH.sub.3 reached                            Adsorbent   (mg-atom/ its amount  5%                                           No.         g)        (mg-atom/g) (min.)                                       ______________________________________                                         A (Control) 0         0            15                                          B (Control) 2.0       0            45                                          C (Control) 0         Na-2.0       50                                          D (Control) 0         K-2.0        65                                          E (Control) 0         Mg-2.0       65                                          F (Control) 0         Ca-2.0       80                                          G (Control) 0         Sr-2.0       85                                          H (Control) 0         Al-2.0       40                                          I (Control) 0         Cr-2.0       70                                          J (Control) 0         Fe-2.0       85                                          K (Control) 0         Ni-2.0       75                                          L (Control) 0         Pb-2.0       80                                           ○1  (The present                                                                   1.0       Na-1.0      610                                          invention)                                                                      ○2  (The present                                                                   1.0       K-1.0       885                                          invention)                                                                      ○3  (The present                                                                   1.0       Mg-1.0      900                                          invention)                                                                      ○4  (The present                                                                   1.0       Ca-1.0      880                                          invention)                                                                      ○5  (The present                                                                   1.0       Sr-1.0      870                                          invention)                                                                      ○6  (The present                                                                   1.0       Al-1.0      730                                          invention)                                                                      ○7  (The present                                                                   1.0       Ti-1.0      700                                          invention)                                                                       ○8 1.0he present                                                                            V-1.0       960                                          invention)                                                                      ○9  (The present                                                                   1.0       Cr-1.0      950                                          invention)                                                                      ○10 1.0he present                                                                            Mn-1.0      880                                          invention)                                                                      ○11 1.0he present                                                                            Fe-1.0      790                                          invention)                                                                      ○12 1.0he present                                                                            Co-1.0      990                                          invention)                                                                      ○13 1.0he present                                                                            Ni-1.0      850                                          invention)                                                                      ○14 1.0he present                                                                            Zn-1.0      750                                          invention)                                                                      ○15 1.0he present                                                                            Cd-1.0      700                                          invention)                                                                      ○16 1.0he present                                                                            Pb-1.0      730                                          invention)                                                                      ○17 0.2he present                                                                            Cr-1.0      450                                          invention)                                                                      ○18 0.5he present                                                                            Cr-1.0      600                                          invention)                                                                      ○19 2.0he present                                                                            Cr-1.0      1050                                         invention)                                                                      ○20 1.0he present                                                                            Pb-1.0      800                                          invention)                                                                      ○21 1.0he present                                                                            Cs-1.0      600                                          invention)                                                                      ○22 1.0he present                                                                            Ba-1.0      630                                          invention)                                                                      ○23 1.0he present                                                                            Na-0.3, Al-0.5                                                                             1050                                         invention)                                                                      ○24 1.0he present                                                                            K-0.3, V-0.5                                                                               1100                                         invention)                                                                      ○25 1.0he present                                                                            K-0.3, Cr-0.5                                                                              1320                                         invention)                                                                      ○26 1.0he present                                                                            K-0.3, Mn-0.5                                                                              1260                                         invention)                                                                      ○27 1.0he present                                                                            K-0.3, Fe-0.5                                                                              1130                                         invention)                                                                      ○28 1.0he present                                                                            Mg-0.3, Co-0.5                                                                             1290                                         invention)                                                                      ○29 1.0he present                                                                            Ca-0.3, Ni-0.5                                                                             1350                                         invention)                                                                      ○30 1.0he present                                                                            K-0.3, Zn-0.5                                                                              1190                                         invention)                                                                      ○31 1.0he present                                                                            Na-0.3, Cd-0.5                                                                             1200                                         invention)                                                                      ○32 1.0he present                                                                            K-0.3, Pb-0.5                                                                              1150                                         invention)                                                                      ○33 0.2he present                                                                            K-0.3, Cr-0.5                                                                              700                                          invention)                                                                      ○34 0.5he present                                                                            K-0.3, Mn-0.5                                                                              930                                          invention)                                                                      ○35 0.2he present                                                                            Mg-0.5, Cr-0.5                                                                             850                                          invention)                                                                      ○36 0.5he present                                                                            Mg-0.5, Cr-0.5                                                                             900                                          invention)                                                                      ○37 1.0he present                                                                            K-0.3, Mg-0.3                                                                              1300                                         invention)                                                                      ○38 1.0he present                                                                            K-0.3, Co-0.5,                                                                             1400                                         invention             Ni-0.5                                                    ○39 1.0he present                                                                            Mg-0.3, Cr-0.5,                                                                            1420                                         invention             Mn-0.5                                                    ○40 1.0he present                                                                            K-0.3, Mg-0.3,                                                                             1510                                         invention             Cr-0.5, Fe-0.25                                          ______________________________________                                     

What is claimed is:
 1. A method for removal of at least one hydride of As, B, P, Sb and Se from a gas containing said hydride and substantially not containing oxygen, which comprises contacting the gas with an activated carbon containing:(1) copper oxide in an amount of 0.1 mg-atom to 3.0 mg-atom as metal per g of activated carbon and (2) at least one of (a), (b) and (c) selected from the group consisting of(a) at least one alkali metal compound, (b) at least one alkaline earth metal compound and (c) at least one compound of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Cd and Pb,the total amount of (2) being 0.2 mg-atom to 4.0 mg-atom as metal per g of activated carbon.
 2. A method as claimed in claim 1, wherein the activated carbon contains:(1) copper oxide and (2) at least one alkali metal compound.
 3. A method as claimed in claim 1, wherein the activated carbon contains:(1) copper oxide and (2) at least one alkaline earth metal compound.
 4. A method as claimed in claim 1, wherein the activated carbon contains:(1) copper oxide and (2) at least one compound of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Cd and Pb.
 5. A method as claimed in claim 1, wherein the activated carbon contains:(1) copper oxide and (2)(a) at least one alkali metal compound and (c) at least one compound of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Cd and Pb.
 6. A method as claimed in claim 1, wherein the activated carbon contains:(1) copper oxide and (2)(a) at least one alkali metal compound, (b) at least one alkaline earth metal compound and (c) at least one compound of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Cd and Pb.
 7. A method as claimed in claim 1, wherein the activated carbon contains:(1) copper oxide and (2)(a) a compound of potassium and (c) a compound of chromium.
 8. A method as claimed in claim 1, wherein the gas is contacted with the activated carbon at a temperature of not more than 200° C. 